Subject: [tsvwg] I-D Action: draft-ietf-tsvwg-rlc-fec-scheme-04.txt

From: [email-masked]
Date: Thu, 17 May 2018 23:51:17 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Transport Area Working Group WG of the IETF.

        Title           : Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC) Schemes for FECFRAME
        Authors         : Vincent Roca
                          Belkacem Teibi
	Filename        : draft-ietf-tsvwg-rlc-fec-scheme-04.txt
	Pages           : 31
	Date            : 2018-05-17

Abstract:
   This document describes two fully-specified Forward Erasure
   Correction (FEC) Schemes for Sliding Window Random Linear Codes
   (RLC), one for RLC over GF(2) (binary case), a second one for RLC
   over GF(2^^8), both of them with the possibility of controlling the
   code density.  They can protect arbitrary media streams along the
   lines defined by FECFRAME extended to sliding window FEC codes.
   These sliding window FEC codes rely on an encoding window that slides
   over the source symbols, generating new repair symbols whenever
   needed.  Compared to block FEC codes, these sliding window FEC codes
   offer key advantages with real-time flows in terms of reduced FEC-
   related latency while often providing improved packet erasure
   recovery capabilities.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-rlc-fec-scheme/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-tsvwg-rlc-fec-scheme-04
https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-rlc-fec-scheme-04

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-tsvwg-rlc-fec-scheme-04

Please note that it may take a couple of minutes from the time of submission
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Internet-Drafts are also available by anonymous FTP at:
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---

From: Vincent Roca <[email-masked]>
Date: Fri, 18 May 2018 09:13:14 +0200

Dear all,

Here is an updated version of our I-D.

- It takes into accounts comments received by Jonathan Detchart
  (added section 3.6. Finite Fields Operations);

- Section 3.1. Possible Parameter Derivations 
  has been significantly improved for more precision;

- It also fixes a small bug (in parameter checks) in 
  section 3.5.  Coding Coefficients Generation Function;

We are not sure we will keep the current PRNG...
Even with the previous fix (i.e., ignoring the first value produced),
the Park-Miler minimal standard PRNG behaves badly when used
with seeds that are in sequence (e.g., the application generates
a repair symbol with seed s and then s+1, etc.) and when mapping
the PRNG output to a small range of value (especially with [0, 15]):
	Ij+1 = A * s (modulo M)
and:
	Ij+1 = A * (s+1) (modulo M)
scaled to [0, 15] have a certain probability to give the same value.
We are  currently experimenting with alternatives. Unfortunately we
only identified this side-effect recently. 

Cheers,

   Vincent and Belkacem

> Le 18 mai 2018 à 08:51, [email-masked] a écrit :
> 
>